1. Field
This document relates to a plasma display apparatus and a driving method thereof.
2. Related Art
In general, a plasma display panel (PDP) applies a reset pulse for initializing a discharge cell, an address pulse for selecting a cell to be discharged, and a sustain pulse for sustaining a discharge of a discharge cell to each electrode by a predetermined number of times according to a gray level value of each subfield and allows a phosphor to emit light by a gas discharge generating through applying of the pulses. The PDP repeats resetting, addressing, and sustaining in each subfield constituting a frame, and it is required to apply an erase pulse for removing wall charges remaining in each electrode side before the each subfield starts in order to improve PDP driving characteristics.
FIG. 1 is a view illustrating a structure of a general PDP.
As shown in FIG. 1, the PDP comprises a front panel 100 and a rear panel 110 that are disposed apart a predetermined distance and coupled in parallel to each other. The front panel 100 is arranged with a plurality of sustain electrode pairs in which a scan electrode 102 and a sustain electrode 103 are formed in pairs on a front glass 101, which is a display surface for displaying an image. The rear panel 110 has a plurality of address electrodes 113 arranged to intersect the plurality of sustain electrode pairs on a rear glass 111 constituting a rear surface.
The front panel 100 comprises pairs of the scan electrode 102 and the sustain electrode 103, which have a transparent electrode (a) made of transparent indium-tin-oxide (ITO) and a bus electrode (b) made of metal, for performing a mutual discharge in one discharge cell and sustaining emission of the cell. The scan electrode 102 and the sustain electrode 103 are covered with at least one upper dielectric layer 104 that limits a discharge current and that insulates each electrode pair. A protective layer 105 deposited with magnesium oxide (MgO) is formed on the upper dielectric layer 104 to facilitate a discharge condition.
The rear panel 110 comprises stripe-type (or well-type) barrier ribs 112, which are arranged in parallel, for forming a plurality of discharge spaces i.e., discharge cells. A plurality of address electrodes 113 for generating vacuum ultraviolet rays by performing an address discharge is arranged in parallel to the barrier ribs 112. Red (R), green (G) and blue (B) phosphors 114 that emit visible rays for displaying an image at an address discharge are coated over an upper surface of the rear panel 110. A lower dielectric layer 115 for protecting the address electrode 113 is formed between the address electrode 113 and the phosphor 114.
A method of representing an image gray level in the PDP is shown in FIG. 2.
FIG. 2 is a diagram illustrating a method of representing an image gray level of a general PDP.
As shown in FIG. 2, in the method of representing an image gray level of a conventional PDP, a frame is divided into several subfields having different number of times of light emitting and each subfield is again divided into a reset period (RPD) for initializing all cells, an address period (APD) for selecting a cell to be discharged, and a sustain period (SPD) for representing a gray level depending on the number of times of discharges. For example, when an image is represented with 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 second is divided into eight subfields (SF1 to SF8), as shown in FIG. 2 and each of the eight subfields (SF1 to SF8) is again divided into the reset period, the address period, and the sustain period.
The duration of the reset period in a subfield is equal to the duration of the reset periods in the remaining subfields. The duration of the address period in a subfield is equal to the duration of the address periods in the remaining subfields. An address discharge for selecting a cell to be discharged is generated by a voltage difference between an address electrode and a transparent electrode, which is a scan electrode. The sustain period increases in a ratio of 2n (n=0, 1, 2, 3, 4, 5, 6, 7) in each subfield. Since the sustain period becomes different in each subfield, a gray level of an image is expressed by adjusting a sustain period of each subfield, i.e., the number of times of a sustain discharge. A driving waveform according to a driving method of the PDP is shown in FIG. 3.
FIG. 3 is a diagram illustrating a driving waveform according to a driving method of a conventional PDP.
As shown in FIG. 3, the PDP is divided into a reset period for initializing all cells, an address period for selecting a cell to be discharged, and a sustain period for sustaining a discharge of the selected cell for driving.
In a setup period (SU) of the reset period, ramp-up waveforms (ramp-up) are simultaneously applied to all scan electrodes (Y). A discharge is generated within discharge cells of an entire screen by the ramp-up waveform. The setup discharge causes positive wall charges to be accumulated on address electrodes (X) and sustain electrodes (Z) and negative wall charges to be accumulated on scan electrodes (Y). In a setdown period (SD) of the reset period, after the ramp-up waveform is applied, a ramp-down waveform (ramp-down) that falls from a positive voltage lower than a peak voltage of the ramp-up waveform up to a ground (GND) voltage or a negative voltage level is applied, whereby a weak erase discharge is generated within the discharge cells and thus some of excessively formed wall charges is erased. Wall charges sufficient for a stable address discharge due to the setdown discharge are uniformly remained within the discharge cells.
In the address period, negative scan pulses (Scan) are sequentially applied to the scan electrodes (Y) and positive data pulses (data) are applied to the address electrodes (X) in synchronization with the scan pulse. As a voltage difference between the scan pulses and the data pulses is added to a wall voltage by wall charges generated in the initialization period, an address discharge is generated within the discharge cells to which the data pulse is applied. Wall charges sufficient for a discharge when a sustain voltage is applied are generated within discharge cells selected by an address discharge. The sustain electrodes (Z) are supplied with a positive DC voltage (Zdc) so that an erroneous discharge is not generated between the sustain electrode (Z) and the scan electrode (Y) by reducing the voltage difference between the sustain electrode (Z) and the scan electrode (Y) during the setdown period and the address period.
In the sustain period, sustain pulses (Sus) are alternately applied to the scan electrodes (Y) and the sustain electrodes (Z). In a discharge cell selected by an address discharge, a sustain discharge, i.e., a display discharge is generated between the scan electrodes (Y) and the sustain electrodes (Z) whenever each sustain pulse is applied as the sustain pulse and the wall voltage within the discharge cell are added.
After the sustain discharge is completed, an erase ramp waveform (Ramp-ers) having a narrow pulse width and a low voltage level is applied to the sustain electrodes (Z) to erase wall charges remaining within the discharge cells of the entire screen.
As described above, as the plasma display apparatus alternately applies positive sustain pulses (sus) to the scan electrode (Y) side and the sustain electrode (Z) side during a sustain period, positive ions are stacked to the address electrode (X) side having a relatively low potential difference. As positive ions relatively heavier than electrons apply ion bombardment to a phosphor layer (114 of FIG. 1) of a rear panel in which address electrodes (X) are formed, a lifetime of the plasma display apparatus is shortened.
Accordingly, as shown in FIG. 4, recently, by allowing the sustain pulses (sus) to have a negative voltage level, a negative sustain type driving in which electrons are stacked in a rear panel in which the scan electrode (Y) and the sustain electrode (Z) are formed, is performed.
FIG. 4 is a diagram illustrating a driving waveform according to a negative sustain driving method of a conventional PDP.
As shown in FIG. 4, a negative sustain pulse (−sus) is alternately applied to the scan electrode (Y) and the sustain electrode (Z) during a sustain period.
Accordingly, as described above, electrons are relatively stacked by the negative sustain pulses (−sus) in the rear panel 110 in which the phosphor layer 114 is formed, whereby ion bombardment applied to the phosphor layer 114 is decreased. However, as the ion bombardment increases in the magnesium oxide (MgO) layer 105 formed in the front panel 100 in a process in which positive ions are stacked, a secondary electron generating rate improves.
That is, by increasing a secondary electron generating amount while preventing damage of the phosphor layer 114, a lifetime of a plasma display apparatus can be extended and a discharge firing voltage can be lowered.
The negative sustain pulse (−sus) can be applied to a long gap structure, which is a new electrode structure.
A conventional interval between electrodes was about 60 to 80 um, but a structure of increasing a light amount passing through an interval between electrodes by widening an interval between electrodes to more than 150 um is referred to as a long gap structure. According to the long gap structure, as a light amount emitted from a phosphor increases, light emitting efficiency can be improved.
In order to represent a long gap structure, the long gap structure is generally formed by reducing a conventional electrode area, i.e., an ITO area. According to the long gap structure, when a discharge is generated between the scan electrode and the sustain electrode, an opposed discharge is generated if a sustain voltage is set to a ground voltage.
The opposed discharge is a discharge between the scan electrode and the data electrode. That is, in the long gap structure, a discharge is generated due to a voltage difference between the scan electrode and the data electrode earlier than a discharge between the scan electrode and the sustain electrode when a voltage difference is generated between the sustain electrode set to a ground voltage and the scan electrode. As describe above, the long gap structure is driven on the assumption of generating of an opposed discharge. Accordingly, a driving method different from a driving method in a conventional surface discharge mode is required.